The present invention relates to a rotary magnetic head device having a pair of thin-film magnetic heads and, more particularly, to a compact, light-weight rotary magnetic head device suitable for a video tape recorder (hereinafter abbreviated as VTR).
In the VTR, in general, a rotary magnetic head device is used. A rotary magnetic head device comprises a pair of cylinders facing each other at an interval and forming a chamber therebetween; a rotating shaft projecting into the cylinders substantially coaxial with the cylinders; a rotor having a pair of magnetic heads each having a gap of a predetermined length at the end thereof and mounted on the shaft in the chamber of the cylinders; and a rotary transformer for coupling the magnetic heads to an external circuit.
FIG. 1 is a plan view of a conventional rotary magnetic head device; FIG. 2 is a side view thereof; and FIG. 3 is an enlarged plan view of a magnetic head. Each of the magnetic heads 10 has: a pair of magnetic cores 12 and 14 made of a magnetic material such as ferrite or sendust, the magnetic cores 12 and 14 opposing each other so as to define a gap G therebetween; windings 16 wound around the distal end portions of the cores 12 and 14, respectively; and a metal base plate 18 on which the cores 12 and 14 are mounted. A rotating shaft 26 is fitted in a rotor 20 to be fixed thereby. The magnetic heads 10 are disposed on a line passing through an axis of the rotating shaft 26 such that their tape contact surfaces face outward with respect to the rotor 20. The magnetic heads 10 are located at substantially the same distance R with respect to the center of rotation of the rotating shaft 26, and are bolted on a surface of the rotor 20. Rotor core 21 of the rotary transformer is mounted on the rotor 20. Two annular grooves are formed on this surface of the rotor core 21 to be concentric with the center of rotation of the rotating shaft 26. Coils 22 and 24 are embedded in these annular grooves, respectively. The coils 22 and 24 serve as the rotor of the rotary transformer. The magnetic heads 10 are connected to the coils 22 and 24, respectively.
In the conventional magnetic head device, the distal ends of the magnetic heads 10 at the sides of their gaps are each spaced apart by the distance R from the center O of rotation of the rotor 20. The magnetic heads 10 must be mounted on the rotor 20 such that the line connecting the distal ends passes through the center of rotation O of the rotor. For this reason, the positions of the magnetic heads 10 relative to the rotor 20 must be finely adjusted on the order of several microns or less when the magnetic heads 10 are bolted on the rotor 20. Precision work calling for skill and concentration using a microscope is required to properly align the heads 10 with the rotor 20. Furthermore, two annular grooves of the rotor core 21 of the rotary transformer and two annular grooves of the stator core of the rotary transformer (not shown) fixed on the cylinder must face each other precisely with a constant gap between the stator core and the rotor core. For this reason, two annular grooves must be precisely formed at predetermined positions of the rotor core 21, resulting in cumbersome, time-consuming work. In addition to the complex operation described above, the magnetic heads 10 must be respectively connected to the coils 22 and 24 by soldering or bonding of lead wires. This work leads to a further complex process in manufacturing the rotary magnetic head device.
On the other hand, there has recently arisen a demand for the development of a video camera having a built-in magnetic recording section within a camera section. In order to achieve this, the magnetic recording section, and hence, the rotary magnetic head device, must be made compact. Therefore, the distance between the center of rotation of the rotating shaft and the distal end of the magnetic head 10 must be less than 40 mm. However, it is very difficult to obtain such a compact structure in a magnetic head device wherein conventional magnetic heads 10 are bolted on the rotor 20.